The invention relates to steam turbines and, more particularly, to a system utilizing dump flow to achieve a performance gain by dumping the steam seal flow back into the turbine.
Thermal power plants such as steam turbines have boilers that burn fuel to make heat. In a power plant, heat energy is conducted into metal pipes, heating water in the pipes until it boils into steam. This steam is fed under high pressure to the turbine. The turbine includes various sections operating at different pressures, including a high pressure section (HP section), an intermediate pressure section (IP section), and a low pressure section (LP section).
In existing machines, steam leaking from the turbine end seal packings is plumbed into a steam seal header. Steam seal leakage increases over time as the end packing teeth wear. After start-up, the machines will self-seal and have a dump flow. In a typical design, the dump flow steam is dumped to the condenser. A performance gain may be realized by dumping the steam seal flow back into the turbine as the steam can expand and do work in the LP section of the turbine.
In a previous design, steam dump flow was routed into the LP turbine. The dump flow, however, is too hot for the LP turbine components, resulting in thermal distortion in the LP hood and diaphragms, which can lead to vibration issues and decreasing performance.
It would be desirable to provide a system that enables steam seal dump re-entry by cooling the steam prior to entering the turbine.